We are developing a procedure for the selection and screening, from a mutagenized population of cultured Chinese Hamster Ovary Cells, of variant cell lines characterized by lower rates of protein degradation. We are currently focused on a procedure based on the assumption that in the absence of amino acids in the medium, continuing protein synthesis will depend on the endogenous supply of amino acids from degradation of prexisting proteins (see: Ledbetter, Scornik and Schwartzman. Selection Procedure for Mutations affecting Protein Degradation. In "Symposium on Intact Human Cell Lines in Study of Inborn Metabolic Diseases", R.P. Cox and Robert Katz, eds., NIH, in press).